In arbitration, a trained and licensed person (or panel of people) are designated to make a decision regarding a disgreement you are having with another party. You are both given the opportunity to make your case and present your evidence to the arbitrator. The arbitrator then makes a decision that is legally binding on both you and the other party. This means you are legally required to do what the arbitrator decides - just like you would be if a judge had told you to do it in court. A decision will always be made if an arbitrator is involved.
A mediator will provide a neutral, confidential environment for two parties who are disgreeing. It gives them a chance to talk things out and try to resolve the issue while in a safe space. The mediator facilitates conversations and problem solving. The mediator does not make legally binding decisions. It is up to you and the other party to decide what is best for your case after having a frank discussion. You do not present evidence and the mediator has no decision making powers. If you don't come to agreement, you take your disgreement to the next step. Keep in mind that if you sign a document agreeing to do something during the mediation process (usually called a Memo of Understanding) it will most likley be upheld by the courts should your disagreement end up in court. In a mediation; so if you don't agree, do not sign anything! Also, you can get up and leave at any time if you are no longer willing to mediate.